using google guava library to hold data for report

Often times when ones work with report (just a typical report), it is pretty common to meet the situation like to hold a list of rows into a data type which has a key and value and maybe a page number. So for java programmer, you will encounter something like this.

public class Report  {

   List<LinkedHashMap<String, String>> rows = new ArrayList<LinkedHashMap<String, String>>();
   private int page;
   
   public static void printReport(Report report) {
		
	List<LinkedHashMap<String, String>> oldReport = report.getOld();
		
	for (LinkedHashMap<String, String> oldRows : oldReport) {
		for (Entry<String, String> entry : oldRows.entrySet()) {
			System.out.print(entry.getValue());
		}
	}
   }

}

So you will have many rows to hold each row in a report and within each row, you have a key and a value. For instance, one the first page of report, you will have a person with first name john and last name doe and age 30. Then you have another row of person, first name dan, last name christensen, age 40, etc. Then to print the report, you basically iterate over the data collections and print out its value.

Is there any other ways, better yet efficient?

So I have google and people suggest using guava and I will take a look at the different feature offer by guava and how it help me in this situation above. So what is google guava?

The Google Guava is an open-source set of common libraries for Java, mainly developed by Google engineers.

This page give a general overview for the common libraries found in google guava. As you notice, there are many features included in this library but for the report above, I will use only two of it. Let's rewrite the above code.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import com.google.common.base.Joiner;
import com.google.common.collect.LinkedHashMultimap;
import com.google.common.collect.LinkedHashMultiset;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multiset;

public class Report {
	
	private int page;
	private List<String> header;
	private Multimap<String, String> rows;
	private Multiset<String> rowsSet;
	
	private List<LinkedHashMap<String, String>> old = new ArrayList<LinkedHashMap<String, String>>();
	
	public Report() {
		page = 0;
		header = new ArrayList<String>();
		rows = LinkedHashMultimap.create();
		rowsSet = LinkedHashMultiset.create();

	}
	
	
	public void getReportFromDS() {
		header.addAll(Arrays.asList("firstName", "LastName", "age"));
		rows.put("2829f395317df0f88597ef288f132827794707af", "john");
		rows.put("2829f395317df0f88597ef288f132827794707af", "doe");
		rows.put("2829f395317df0f88597ef288f132827794707af", "30");
		rows.put("d94c2ddf2a4817e5c9a56db45d41ed876e823fcf", "dan");
		rows.put("d94c2ddf2a4817e5c9a56db45d41ed876e823fcf", "christensen");
		rows.put("d94c2ddf2a4817e5c9a56db45d41ed876e823fcf", "40");
		rows.put("1fd23a55e9780810d2e6f0ec9ba1ddb99827e4cf", "chai");
		rows.put("1fd23a55e9780810d2e6f0ec9ba1ddb99827e4cf", "lenny");
		rows.put("1fd23a55e9780810d2e6f0ec9ba1ddb99827e4cf", "20");
	}
	
	public int getPage() {
		return page;
	}


	public List<String> getHeader() {
		return header;
	}


	public Multimap<String, String> getRows() {
		return rows;
	}
	
	public List<LinkedHashMap<String, String>> getOld() {
		return old;
	}


	public static void printReport(Report report) {
		Joiner joiner = Joiner.on(", ");
		String headers = joiner.join(report.getHeader());
		
		System.out.println(headers);
		Map<String, Collection<String>> rows = report.getRows().asMap();
		
		for (Entry<String, Collection<String>> row : rows.entrySet()) {
			
			String line = joiner.join(row.getValue().iterator());
			System.out.println(line);
		}
		
		List<LinkedHashMap<String, String>> oldReport = report.getOld();
		
		for (LinkedHashMap<String, String> oldRows : oldReport) {
			for (Entry<String, String> entry : oldRows.entrySet()) {
				System.out.print(entry.getValue());
			}
		}
	}
	

	public static void main(String[] args) {
		Report sampleReport = new Report();
		sampleReport.getReportFromDS();
		printReport(sampleReport);
	}

}

As noted from the full code above, it contain the constructor to initialize the objects. Then a method getReportFromDS(), you could probably get from your data source like database. Then we have getter methods and a static method to print the report. If you run this app, you notice it print out the report header, and then rows.

There is a class which join the string together with just two lines. Even better you can make it a line ;-) using Joinner. To print each row of sample report, you can using a for loop but only a for loop. Then you can join the value of the row and print out the row. Less codes and more readability. If you measure the object sampleReport, I guess is much use less memory footprint.

That's it, just two goodies features from google guava, I suggest you read on different features offered and fully use this great library.13